Production of magnetic material



Patented Dec. 22, 1942 PRODUCTION F MAGNETIC MATERIAL Evert JohannesWillem Verweij, Jan Hendrik de Boer, and Theodorus Antonius Spoor,Eind-" hoven, Netherlands; vested in the Alien Property Custodian NoDrawing. Original application April 26, 1937.

Serial No. 139,000.

Divided and this application November 10, 1939, Serial No. 303,816. In

Germany April 29, 1936 Claims. (Cl. 117-400) This application is adivision of United States patent application Serial No. 139,000. filedApril 26, 1937, now Patent No. 2,232,352, entitled Production ofmagnetic material and of magnetic cores therefrom.

It is common to produce magnetic cores for intermediate and highfrequency purposes from finely powdered magnetic material such as ironor ferromagnetic alloys, by compressing the particles by means of abinding agent to form a solid material. For the purpose of avoidingconductive relative contact between the said particles, various methodshave been proposed according to which these particles are provided,prior to squeezing, with an insulating film. Thus, for example, it hasbeen described to superficially attack the particles chemically bytreating iron particles with a, phosphoric acid solution or a solutionof a phosphoric acid compound, a ferric phosphate film being formed onthe said particles due to the reaction with the iron.

According to the invention. in contradistinction thereto, a film of aphosphoric acid metal compound is mounted on the magnetic particleswithout these particles assisting genetically in the film formation,which can be ensured by precipitation of the phosphoric acid metalcompound from a dispersion which practically does not attack themagnetic particles.

The invention offers the advantage that shape and d mensions of themagnetic particles remain unaltered since for the formation of theinsulating film no material of the magnetic particles is chemicallytransformed. This is particularly conductive to uniform manufacturesince the quantity of insulating material per particle of the magneticmaterial can be controlled without any difficulty to a suificientlyaccurate extent, which is substantially more diflicult with chemicalattack of the surface since the rate and the uniformity of the chemicalattack per particle can only be controlled with dimculty. The fact thatin accordance with the invention no gas development as a result ofchemical reaction arises is also conductive to uniformity.

The invention is consequently particularly adapted for use with magneticparticles the dimensions of which are in the order of magnitude of a fewf, the thickness of the insulating films to be obtained not exceeding 20m Since in accordance with the invention the magnetic particles havebeen provided with a thin insulating film, the magnetic powder thusobtained can be given any shape by compression.

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In order to increase the mechanical strength of the magnet core abinding agent may be used with advantage in a manner known per se afterthe insulating film is mounted. For this purpose, use may be made, forexample of a synthetic resin which may be capable of being hardened. Inthe use of a resin capable of being hardened, even distribution of themagnetic particles in the final product may be assisted by grinding thematerial after mixture with the resin, by next giving it at ordinarytemperatures the desired shape and by then heating it to cause it toharden.

Example I 1 kg. of magnetic powder is introduced into 1 litre of a 2normal solution of aqua-ammonia containing 60 milliequivalents of zincion and 60 milliequivalents of phosphate ion. The excess of aqua-ammoniais then removed by boiling while shaking continuously so that all thezinc phosphate present in the solution is precipitated on the surface ofthe particles. After being filtered and dried, the powder is squeezedinto the desired shape at a pressure of about 5000 ken/cm Example If 1kg. of magnetic powder is intimately mixed with about cm. of a 2 normalsolution of aqua-ammonia containing 30 milliequivalents of zinc ion and45 milliequivalents of phosphate ion per 100 cm.-". The paste thusobtained is kneaded while evaporating the excess of aqua-ammonia andwater, which may be effected while heating to a low extent or in vacuoat ordinary temperatures. The material is then completely dried andground to form a powder which is mixed with an alcohol solutioncontaining 60 grams of a hardening phenolformaldehyde condensationproduct. After volatilization of the solvent the powdering operation isrenewed and the powder is then squeezed at C. into the desired shape, itbeing possible to apply a squeezing pressure of 1500 kg./cm.

In order to avoid the presence of other electrolytes which would affectthe properties of the core, the ammoniacal zinc phosphate solution maybe obtained by newly precipitated zinc hydroxide being dissolved in aconcentratedsolution of aqua-ammonia, by a dilute phosphoric acidsolution being next added and by the solution being then given thedesired concentration by dilution.

Example III 1 kg. of magnetic powder is intimately mixed with aboutlOOcm. of a weakly-acid ferric phosphate solution containing 30milliequivalents of ferri-ion and 30 milliequivalents of phosphate ionper 100 cm. The paste is evaporated and dried, while kneading, in themanner described in the second example. The material thus oh- I gainedis reduced to the form of a powder and Example IV 1 kg. of magneticpowder is intimately mixed,

with about 100 cm. of a 2 normal solution of aqua-ammonia containing 30milliequivalents of cupri-ion and 45 milliequivalents of phosphate ionper 100 cm. and the mixture is evaporated to dryness and powdered, whilekneading, in the manner described in the second example. -The powder isagitated in a solution containing 60 grams of a hardeningphenolformaldehyde condensation product and is then evaporated todryness while shaking. The material thus obtained is reduced to the formof a powder and then squeezed at ordinary temperatures at a pressure ofabout 5000 kg./cm.'*. The cores thus obtained are hardened in a furnaceby heating for three hours at 130 C.

The quantities, indicated in the examples described, of ,the substancesused are chosen to accord with the specific weight of the iron and anaverage size of the particles of 3 1. as possessed by certain knowncommercial powdered iron by means of which the invention yieldsparticularly favorable results.

We claim:

1. The steps in a process of providing particles of ferro-magneticmaterial with a coating of insulation material substantially solely byprecipitation on the outer surface of the particles, of an insulationmaterial derived from a chemical compound and without causing anysubstantial reaction between the particles and the chemical compound,which comprise intimately mixing comminuted ferro-magnetic material witha compound comprising a 2 normal solution of aqua-ammonia containingzinc ion and phosphate ion, and drying the mixture while subjecting itto substantially continuous agitation whereby zinc phosphate is causedto be precipitated on the outer surface of the particles.

2. The process described in claim 1 characterized by that the drying ofthe mixture is accomplished by applying heat thereto.

3. The steps in the method of providing particles of ferro-magneticmaterial with a coating of insulation material substantially solely byprecipitation on the outer surface of the particles of an insulationmaterial derived from a chemical compound and without causing anysubstantial reaction between the particles and the chemical compound,which comprise intimately mixing in the proportion of about one kilogramof comminuted ferro-magnetic material with a compound comprising onelitre of 2 normal solution of aqua-ammonia containing sixtymilliequivalents of zinc ion and sixty milliequivalents of phosphateion, drying the mixture while subjecting it to substantially continuousagitation to thereby precipitate zinc phosphate on the surface of themagnetic particles.

4. The process described in claim 1 characterized by that the mixture ismade by mixing with each kilogram of magnetic material approximately onehundred cubic centimeters of the two normal solution of aqua-ammoniacontaining thirty milliequivalents of the zinc ion and fortyfivemilliequivalents of the phosphate ion whereby the mixture is in the formof a paste and by that the drying of the resulting mixture isaccomplished by heating the same to a comparatively low temperature andkneading it to provide for proper mixing thereof.

5. The steps in a. process of providing particles of ferro-magneticmaterial with a coating of insulation material substantially solely byprecipitation on the outer surface of the particles of an insulationmaterial derived from a chemical compound and without causing anysubstantial reaction between the particles and the chemical compound,which comprise intimately: mixing comminuted magnetic material with aphosphoric acid metal compound comprising aqua-ammonia phosphate-ion andone of the elements of the group consisting of zinc-ion and cupri-ion,and treating the resulting mixture so as to form around each of saidparticles a thin layer of said compound.

EVERT J OHANNES WILLEM VERWEIJ. JAN HENDRIK vs BOER. THEODORUS ANTONIUSSPOOR.

